I have an O.S. .91 FX in my UCanDo 3D. I run 10% nitro, and had some pre-ignition problems (knocking). Noticeably worse on down lines. A friend with the same engine suggested adding a second head gasket which I did. While this reduced the amount of knocking, it still occurs. My UCD hovers quite nicely with the .91, but it doesn't rocket out of a hover like I thought it would. I use a 15x6 APC prop and the plane weighs 8.2 lbs. Did putting in the extra gasket reduce HP? Any suggestions as to how I can maximize power (or ability to rocket out of a hover) without increasing the pre-igniton problem?